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  1. #1
    Active Member Two Rings
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    Engine temp always cold

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    Anyone got any ideas on why my temp gauge reads cold all the time even when driving for long distances? The strange part is that if i go to the store and leave the car for a few minutes, when i return and start it the gauge reads operating temp then dives back to cold after a couple minutes. Thermostat sticks open? I bought the car in atlanta so maybe the thermostat has been adjusted?


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  2. #2
    Veteran Member Four Rings Audibot's Avatar
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    If the thermostat was stuck open, it should eventually reach operating temperature after long period of time. You can check/feel the upper rad hose--if it's hot, your coolant is properly circulating and the thermostat is working.

    If it's hot, then the coolant temperature sensor (green one) is probably bad. Maybe gets intermittent readings or something.
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  3. #3
    Established Member Two Rings
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    I agree with Audibot. However, it's also possible the wires on the plug going to the coolant temp sensor are bad or going bad. The insulation on those wires tend to get baked from engine heat then flake off because Audi uses shitty wiring in the engine compartment. This could lead to a wiring short or broken wires...but not sure if the short would cause it to show cold all the time on the gauge. If you do have flaking wire insulation, if the metal part of the wire is not broken yet, you could clean the connector with some break clean or alcohol, then coat the wires with some high temp RTV to re insulate them, just make sure you don't "glue" the exposed wires together so they are always shorting. You can also buy new replacement connectors that you can splice in to replace the old connector and wires with as well.

  4. #4
    Active Member Two Rings
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    Quote Originally Posted by Audibot View Post
    If the thermostat was stuck open, it should eventually reach operating temperature after long period of time. You can check/feel the upper rad hose--if it's hot, your coolant is properly circulating and the thermostat is working.

    If it's hot, then the coolant temperature sensor (green one) is probably bad. Maybe gets intermittent readings or something.

    Just took her for a spin and that hose is nice and warm. Hanks for the tip guess i have to find a new sensor and see if that works.


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  5. #5
    Active Member Two Rings
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    Quote Originally Posted by mobildetroit View Post
    I agree with Audibot. However, it's also possible the wires on the plug going to the coolant temp sensor are bad or going bad. The insulation on those wires tend to get baked from engine heat then flake off because Audi uses shitty wiring in the engine compartment. This could lead to a wiring short or broken wires...but not sure if the short would cause it to show cold all the time on the gauge. If you do have flaking wire insulation, if the metal part of the wire is not broken yet, you could clean the connector with some break clean or alcohol, then coat the wires with some high temp RTV to re insulate them, just make sure you don't "glue" the exposed wires together so they are always shorting. You can also buy new replacement connectors that you can splice in to replace the old connector and wires with as well.
    Ill check that maybe save a little money. Pretty sure its something to do with the sensor because the car works fine besides that gauge.


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  6. #6
    Established Member Two Rings
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    Hold the recirculation button on AC and then press the UP arrow / UP vent activation, the AC diag menu will come up , using the temp controls go to number 49, then press the recirc button again, this will display your actual coolant temp. Report back to see what it says.
    2000 Audi A4 B5 Avant - 1.8 N/A ARG bottom end, AEB Head ( cams, valves, springs etc.) , big port gasket matched N/A intake manifold . Planning turbo conversion soonTM .

  7. #7
    Active Member Two Rings
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    Quote Originally Posted by Blazius View Post
    Hold the recirculation button on AC and then press the UP arrow / UP vent activation, the AC diag menu will come up , using the temp controls go to number 49, then press the recirc button again, this will display your actual coolant temp. Report back to see what it says.
    will do in the morning. if the sensor is bad it will read low correct?


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  8. #8
    Established Member Two Rings
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    It should read according to gauge, but it will read below 60C unlike the gauge too. If there is something really wrong with the gauge or sensor you should be able to see it. Next step would be checking the sensor with a multimeter according to the service manual :)
    2000 Audi A4 B5 Avant - 1.8 N/A ARG bottom end, AEB Head ( cams, valves, springs etc.) , big port gasket matched N/A intake manifold . Planning turbo conversion soonTM .

  9. #9
    Active Member Two Rings
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    Ok heres the update. Been driving about 20 minutes now and the climate control reads the engine temp at a steady 90C for the past 10 minutes. Gauge in the dash holding at C. So what gives?


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  10. #10
    Veteran Member Four Rings Audibot's Avatar
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    Quote Originally Posted by nathan88 View Post
    Ok heres the update. Been driving about 20 minutes now and the climate control reads the engine temp at a steady 90C for the past 10 minutes. Gauge in the dash holding at C. So what gives?


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    Cluster broken? Any chance you have access to VCDS or similar that can do a needle sweep?
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  11. #11
    Established Member Two Rings
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    Quote Originally Posted by nathan88 View Post
    Ok heres the update. Been driving about 20 minutes now and the climate control reads the engine temp at a steady 90C for the past 10 minutes. Gauge in the dash holding at C. So what gives?


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    If number 49 ( not 51 ) on climate control reads 90 C then your CTS should be good, but just to double check with multimeter at 90C , the resistance of the coolant sensor should be around 200-300. If that is right, then either your gauge is broken , or the wires that lead to it or the other temp sensor on lower radiator is messed up.

    EDIT: As the above post says, do a needle sweep with VCDS , I believe its under Instrument block , then output test.
    2000 Audi A4 B5 Avant - 1.8 N/A ARG bottom end, AEB Head ( cams, valves, springs etc.) , big port gasket matched N/A intake manifold . Planning turbo conversion soonTM .

  12. #12
    Active Member Two Rings
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    Quote Originally Posted by Blazius View Post
    If number 49 ( not 51 ) on climate control reads 90 C then your CTS should be good, but just to double check with multimeter at 90C , the resistance of the coolant sensor should be around 200-300. If that is right, then either your gauge is broken , or the wires that lead to it or the other temp sensor on lower radiator is messed up.

    EDIT: As the above post says, do a needle sweep with VCDS , I believe its under Instrument block , then output test.
    what is different about 49 does it just read another sensor?


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  13. #13
    Established Member Two Rings
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    Quote Originally Posted by nathan88 View Post
    what is different about 49 does it just read another sensor?


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    block/number 49 is the direct CTS temp , if you read 51 its almost always going to show 90 C , which is not right ( engine temp sensor or something like that )
    2000 Audi A4 B5 Avant - 1.8 N/A ARG bottom end, AEB Head ( cams, valves, springs etc.) , big port gasket matched N/A intake manifold . Planning turbo conversion soonTM .

  14. #14
    Active Member Two Rings
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    Engine temp always cold

    oh ok...driving about 15 minutes and it peaked at around 68C when sitting still. time to check the sensor with a multimeter?
    Edit: my oil temp gauge is the same way forgot to mention, dunno if that means anything for ya


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    Last edited by nathan88; 12-04-2018 at 04:12 PM.

  15. #15
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    Quote Originally Posted by nathan88 View Post
    oh ok...driving about 15 minutes and it peaked at around 68C when sitting still. time to check the sensor with a multimeter?
    Edit: my oil temp gauge is the same way forgot to mention, dunno if that means anything for ya


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    So as soon as you start driving temp dropped ? What about if you try to use heat? do that while driving and report back.
    2000 Audi A4 B5 Avant - 1.8 N/A ARG bottom end, AEB Head ( cams, valves, springs etc.) , big port gasket matched N/A intake manifold . Planning turbo conversion soonTM .

  16. #16
    Active Member Two Rings
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    Quote Originally Posted by Blazius View Post
    So as soon as you start driving temp dropped ? What about if you try to use heat? do that while driving and report back.
    Heat works fine, temp drops about 5-10 i think due to the radiator being cooled by airflow right?



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  17. #17
    Established Member Two Rings
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    Quote Originally Posted by nathan88 View Post
    Heat works fine, temp drops about 5-10 i think due to the radiator being cooled by airflow right?



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    Yes but I had the exact same symptoms, if you cannot warm your car up more than 68 C , or 58 C when using heat , you need to change your thermostat. I had this same issue 2 days ago after head swap. You will have to completely drain coolant from radiator drain and water pump drain, change thermostat to brand new one , fill up coolant and bleed it @ heater core output bleed valve.
    2000 Audi A4 B5 Avant - 1.8 N/A ARG bottom end, AEB Head ( cams, valves, springs etc.) , big port gasket matched N/A intake manifold . Planning turbo conversion soonTM .

  18. #18
    Veteran Member Four Rings RENOxDECEPTION's Avatar
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    Quote Originally Posted by nathan88 View Post
    Ok heres the update. Been driving about 20 minutes now and the climate control reads the engine temp at a steady 90C for the past 10 minutes. Gauge in the dash holding at C. So what gives?


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    The coolant temp sensor unit (the one between your engine and the false firewall) has two sensor elements in it, one for the ECU and one for the cluster (that's why it has 4 pins).

    That being said it is likely your sensor needs replacing (or possibly the wiring, but sensor is more suspect and susceptible to failure).

    Funny, I just said something similar in the last thread I responded to...

    The other coolant sensor on the radiator controls the radiator fan, I think (someone else can verify).

    edit: The above only applies if you have a green four pin CTS
    Last edited by RENOxDECEPTION; 12-05-2018 at 01:21 AM.

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